**10.4 Helminth vaccines in focus**

Global data on parasitic helminthes speaks loudly of the livestock diseases that affect many area of the world, including Europe. Their infections are related to huge economic losses in loss of fertility, production and body weight [152]. Cumulative responsible statistics show that more than 55% of livestock suffer from these infections outcome. It causes diseases in Europe and cause highly significant losses in productivity and welfare in animals and then in humans and welfare problems globally. Yearly estimates show that in liver fluke (*Fasciola hepatica*) infections up to US \$3 billion per annum are lost [153]. Conservative estimates in the United Kingdom show that gastrointestinal (GI) helminthic infections to sheep industry shares losses of more than £84 million per annum [154]. These infections are traditionally controlled by administration of various anthelmintic drugs [155]. Naïve practice resulted in development of resistance to these medicines. Recent documentations for sheep farming, particularly in New Zealand, Australia and Brazil, showed that Multi Drug resistance (MDR) is much elaborative phenomenon worldwide and have upward trend [156]. Development of these vaccines started some 50 years ago. Most helminth component formulating and their administration showed that they effectively interrupt the dynamic morphological and antigenic changes during parasites life cycle of the worms and can be used as controlling tool [157]. Many helminthes share much sophisticated evasive immune mechanism that is discussed already in detail. This quality of worms make them very hard for scientists to move forward to develop efficient vaccine candidates [158]. Many efforts to develop anthelminthic vaccines in livestock started many years back with limited success [159]. As discussed in detail above, elusive behavior of worms does not provide adequate long-lasting protection at all stages of helminthic maturation [160]. Vaccines provide manifold benefits on improving animal health, welfare and control of animal infection. The use of vaccine also addresses resistance to acaricides, antibiotics and anthelminthic medicinal solutions [158].

At present, there tend to be two strategies to effectively develop vaccine; (i) attenuated and (ii) hidden antigen [159].

## **10.5 Attenuated vaccines**

These vaccines are developed and used after irradiating L3 larval stage that prevents development of mature adult worms. This protection could reach up to 98% *in vitro* with two experimental doses. Attenuated larval *Dictyocaulus filaria* (sheep lungworm) name "DIFIL" for *Dictyocaulus filaria* larva is effectively used in India since 1981 [160]. A similar approaches are used to develop other vaccines.
